Deflection circuit



4 Filed Dc. 3l, 1953 Sept. 10, 1957 A. C. LUTHER, JR-

DEFLECTION CIRCUIT 2 Sheets-Sheet l Xffy g..

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A TII'ORNE 1 Sept. 10, 1957 A. c. LUTHER, JR 2,806,176

' vDEFLECTION CIRCUIT Filed Deo. 51, 195s 2 sheets-sheet 2 Bilk; ll-I j ff Maza/@5k v ATTORNEY,

United @rates Patent 2,3%,176 Patented Sept. l0, 1957 ffice starre nurtncrroN cmeurr Arch C. Luther, r., Merchantville, N. l., assigner to Radio Corporation of America, a corporation of Delaware Appia-.insa December si, 195s, sensi No. 401,676

3 Claims. (Cl. 315-27) This invention relates to television systems and more particularly to circuits for obtaining linear deflection of an electron beam in a cathode ray tube.

In present television practice, the image in a cathode ray tube is scanned by an electron beam which traces successive lines of a raster. In a television camera, an optical image is focused upon a photo-sensitive screen to form an electronic image on a target area, and a modulated Video signal results from an electron beam which traces a raster upon the target area. In a television receiver, the modulated vidco signal is used to control the intensity of an electron beam which scans a raster on a fluorescent screen thereby reproducing the image. The raster traced in the kinescope of the television receiver must have the same configuration as that traced in the camera tube of the television transmitter. The circuitry necessary for detiecting the electron beam to scan these rasters may be the same or similar in both the camera and the receiver.

To accomplish the deflection of an electron beam, a deflection yoke Winding mounted about the neck of the cathode ray tube is excited by sawtooth waves of current which produces a varying magnetic field in the path of the electron beam. The sawtooth deliection Wave is generated by a relaxation oscillator which may be locked-in to a source of scanning synchronizing pulses and caused to operate in synchronism with the pulse source. The output of the relaxation oscillator is a sawtooth voltage wave. Since it is necessary to supply the deflection yoke windings with a saWtooth wave of current, it is necessary to couple the deflection yoke to the relaxation osciiiator by means of an amplifier. It is desirable that this amplifier have a low impedance output circuit to properly match the irnpedance of the deflection yoke. On the other hand, this amplifier should have a high impedance input so that the relaxation oscillator will not be unduly loaded and caused to yield a non-linear waveform. The relaxation oscillator should likewise have a high impedance input so the source of synchronizing pulses will not be unduly loaded.

It is an object of this invention to provide an improved television deection system which is suitable for use with either a television camera or a television receiver.

A further object of this invention is to provide a television deflection system which is simplified and economical to manufacture.

A further object of this invention is to provide a deilection circuit which may furnish deliection waves to a low impedance deflection yoke Winding, and which will have a high impedance input for connection to a synchronizing signal pulse source.

According to this invention, the deflection circuit coinprises a relaxation oscillator coupled to a cathode-follower amplifying stage. A feedback path is used to obtain good sawtcoth linearity. Because the output of the cathodefollower stage presents a low impedance to its load, it will be suitably matched to the deflection yoke winding which may be transformer-coupled to or directly driven by the cathode-follower.

Other objects of this invention will become apparent upon a reading of the following specification and an inspection of the accompanying drawing in which:

Figure 1 shows by block diagram a television receiving circuit which includes by circuit diagram one form of a simplified deflection circuit made in accordance with the teachings of this invention;

Figure 2 illustrates by block and circuit diagram a television transmitting circuit including one form of deection circuit as it may be used with an image orthicon in a television camera; and

Figure 3 shows by circuit diagram a deflection circuit involving the teachings of this invention for use with a vidicon television camera tube.

In the various figures of the drawing similar elements are designated by the same numeral.

Referring to Figure 1 in more detail, there is seen the circuit for a television receiver involving one form of this invention. Incoming video signals are received by the antenna 11 and the television receiver 13 which includes a radio frequency section, a converter section, a local oscillator section `and an intermediate frequency amplifier. A sound channel is indicated by the speaker symbol I5. A

signals to the synchronizing signal separator 21. The

synchronizing signal furnishes synchronizing pulses to the;

horizontal deliection circuit 23 and to a vertical deflection circuit which is shown schematically. A deflection yokey 27 is fitted around the neck of the cathode ray tube 19 and receives deliection waves of current from the horizontal deflection circuit 23 and the vertical deflection circuit by connections at X-X and Y--Y. The elements referred to above may take the form presently employed in commercially available television receivers. One such television receiver is described in the RCA Review for March 1947 beginning at page 58.

Vertical synchronizing pulses 22 from the synchronizing signal separator are applied to a blocking oscillator which includes an electron discharge tube V1. The control electrode of this tube is coupled to the anode circuit by a transformer 24 and a coupling capacitor 25. The frequency of this oscillator may be varied by Varying the grid resistor 26 which constitutes a vertical hold control. When the frequency is adjusted to a value equal to or slightly less than that of the synchronizing pulses 22, the oscillator will lock in with the incoming synchronizing signal.

Triode V1 is normally cut o during which time a capacitor 29 is slowly charged by a B-fvoltage which is; applied through a series resistance including resistors 3L 33 and 35. During the pulse interval, the discharge tube: V1 conducts and the capacitor 29 is abruptly discharged., A sawtooth deflection wave of voltage 37 is generated as a result of the gradual charging and the abrupt discharging of capacitor 29. This sawtooth wave is applied to the grid of a cathode follower triode V2. The output of the cathode follower is coupled to the yoke windings 27 by a transformer 39. Capacitor 41 provides a positive feedback path from the cathode output of triode V2 to the sawtooth wave generating output of the discharge tube V1. This positive feedback path serves to improve linearity of the generated sawtooth voltage.

It is sometimes diiiicult to obtain good low frequency response in a deflection circuit employing transformer coupling between the deflection yoke and the sawtooth wave generator. If the proper low frequency voltage wave shape can be obtained in the primary of the transformer, a secondary voltage will be essentially the same shape. Therefore, driving a transformer with a cathode follower will produce an extended low frequency response because the low output impedance of the cathode follower insures that the proper voltage will be maintained acrossv the transformer primary even though the magnetizing inductance draws a large proportion of the current from Y the circuit. Consequently, a Vgood voltage wavefor'mcan 'be impressed upon theI grid. of thecathode follower and the yoke will havea corresponding linearsawtooth current ilow.

In Figure 2, an image is focused upon ,anY image orthicon camera tube 43 by an optical' system 45. The deflection yoke windings 27'ca`use an electron beam to scan the image. A modulated videosignall is thereby obtained. Thismodulated video signal is amplified by a video amect the electron beam in a vidicon tube 75- l lated video signal is taken from the vidicon tube 75 by` the television transmitter 49 wherein Va, composite video pliiier 47 and is transmitted by a television transmitter Y 49,; A synchronizing signallpulse generator 51 generates horizontal and Vertical blankingpulses for the transmitter and synchronizing pulsesto key the horizontal andvertical deflection circuits. VDetails concerning the elements of the television transmission system referred to above may be found well described in the publishedart.`

Television transmitting equipment is described in the book entitled, Principles of Television Engineering by Fink published by the McGraw Hill Book Co., Inc.

The vertical deflection circuit functions in a manner similar4 to that of the circuit shownin Figure 1. Capaci- Vtors 53 and 55 are charged slowly through a resistive cir- Y cuit comprising resistors 31, 33, 3S, and 57 and discharged abruptly through the discharge tube V1. The sawtooth wave thereby generated is impressed upon the grid of the cathode follower V2 by the capacitive coupling 59.` Positive feedback is provided through capacitor 41. Resistor 61, resistor 54V and capacitor 63 are used to bias the cathode follower V2. Resistor 57 ismade'adjustable in this circuit Vto provide a size control 'for the scanned raster. A centering,adjustmentforfthe raster is provided by the potential dividing resistor 65 which permits direct current to flow'through the yoke windings.`

Second order compensation has been .introduced into Vthis circuitV to correct for the fact that-the lcathode follower outputV stage has a gain less than unity. A resistor 67 is av compensating element to return the cathode biased ,voltage to a center tap of the discharge capacitors 53 and This circuit is particularly advantageous in a color television camera where it is desired to drive 3gyoke'windings in parallel. Since this circuit-with its-W impedance presents a well regulated voltagefoutput, the currents in the Y 3 yokes can be individually adjusted'withpractically no interaction. This Ais not a characteristic' of thercurrent-V regulating circuits. which are presently commonly employed in television cameras.

This invention has been adaptedfor,deflection of YtheVV electron beam in the vidicon camera as-shown by Figure 3. In the circuit shown-inFigureS, negative' synchroniz-l ing pulses are impressed uponwthe gridfof a triode 69 which ampliiies the synchronizing pulses land reversesrtheirV phase. The positive pulses appearing at the plate of triode 69 `are coupled to vrthe grid offthe dischargetube V1 by capacitor 71;` .Int theembodiment ofthe invention shown in Figure 3, the 5triodes-.69and-V1 have beenenclosed within the same evacuated envelope. Y

Sawtooth deflection waves of voltage are developed by the slow charging-and abruptdischarging of capacitors 53 and 55. The charging circuit includes resistors 33Yand 35 whichv couplethe charging capacitors to the B-I- voltage;

The 'discharging circuit for capacitors 53 and 55 isfa pathto ground through the triode V1. e

Y The cathode follower tube V2is likewise a twin triode,

butinthe form .of th e invention illustrated, the triode Y elements are connected Vin parallel to increase the power capacity` of the tube.A Resistor 73 forms-theload im peclanceV 'of' Vthe cathode follower V2 and, the vertical de,- flection yoke windings arecOupIedtothe cathode follower injshuntjwithresistor, 73., In the embodiment of the `invention illustrated, the sawtooth wave is used to deof the raster in the vidicon.

desirable to drive three separatedeection yokewindings Y in parallel. A*Since the deflection circuits described present-essentially a voltage source output with a low impedance tothe'connected loads, each individual Vload can be adjusted with practically nointeractio'nwith the otherVV loads.V

Whatisclaimedis: f

l. A system for deflecting an electron beam inea'telee. vision'image translating device, lincluding a cathode followerfelekctron' discharge device having cathode, grid and anodeelect'rodes; a low impedance circuit comprising a resistance* device: and a device having a resistive compo- Y nent connected-between said cathode electrode and a'point ofiixed'pbten'tial, means to couple deflection system Y' windings to-saiddevice having a resistive component, a first resistor and arsecond'resistor and'arst capacitor anda secondV capacitorconnectedn serie's'in the order named between a point; of iixed positive potential and a pointV of fixed reference potential,V a pulse translating tube having a cathode,V a grid and an anode, the anode being coupled tothe junction between a resistor and'acapacitor, a capacitor connecting thejunction of said Ii'r'st Vand second resistors to a terminal of the resistance device connected tojthe cathode of said discharge device, another capacitor connecting the junction of a resistor and a capacitor of.VV said series circuit to the grid `electrode of Ysaidfdischarge device, a resistor connected between the junction of said irst and second capacitors and a'terminal of 'theresistance Y device connected tosaid VcathodeV electrode, a'nd'aA further resistor connecting the gridz electrode anda point on'saidv resistance device connectedito saidcathode-electrode. n

2. A system for deflecting anelectronbeam: in 'a tele-` Y` vision image reproducingdevice, including a'cathode fol` lower electron discharge devicehavingV cathode, grid Vand anode electrodes, Va low impedance circuit comprising a cathode resistor and the primaryr'windingof a transformer connected between said cathode electrode and a pointiof ixed reference potential, Ua secondary winding on said transformer to couplev deflection systemwindings to said primary winding, a first resistor and asecond resistor and a first capacitor and as econd capacitor* and a .resistive device connected-in series in the order named between said point of fixed positive potential and a point jof fixed reference potential, a pulse translating tube having a cath ode, a grid and an anode, the anode being coupledV to the junction between a resistor andl a capacitor,V a capacitor connecting the junction of said resistorsV to the terminal'rof said iirst and second cathode resistor remote fromV the-r cathode of said discharge device, another capacitor con# necting said junction of a resistor and a capacitor of said series circuit to the grid electrode of said discharge device, aV resistor connecting the junction Vbetween said capacitors to said terminal of the'cathde resistor remote Y from said iirst and second Vcathode electrode, and a furf ther resistor connectingtheV grid electrodeto the terminal of the cathode resistor remote from said cathode electrode.Y

3. A systemfor deflecting an electron beam in atelevision image scanning device, including a cathode follower electron discharge device having cathode, grid and anode electrodes, a low impedance circuit comprising a firstV re- The modu- 5 sistor, a second resistor and a third resistor connected in series in the order named between said cathode electrode and a point of xed reference potential, means to couple deilection system windings across said third resistor, a fourth resistor and a fifth resistor and a irst capacitor and a second capacitor connected in series in the order named between a point of xed positive potential and said point of fixed reference potential, a pulse translating tube having a cathode, a grid and an anode, the anode being coupled to the junction between said fth resistor and said first capacitor, a capacitor connecting the junction of said fourth and fth resistors to the cathode of said discharge device, another capacitor connecting said junction between References Cited in the file of this patent UNITED STATES PATENTS 2,248,975 Faudell July 15, 1941 2,482,150 Bocciarelli Sept. 20, 1949 2,536,853 Moore et a1 Jan. 2, 1951 

